On 11/15/12 3:05 PM, David Nadlinger wrote:
On Thursday, 15 November 2012 at 22:57:54 UTC, Andrei Alexandrescu wrote:
On 11/15/12 1:29 PM, David Nadlinger wrote:
On Wednesday, 14 November 2012 at 17:54:16 UTC, Andrei Alexandrescu
wrote:
That is correct. My point is that compiler implementers would follow
some specification. That specification would contain informationt hat
atomicLoad and atomicStore must have special properties that put them
apart from any other functions.
What are these special properties? Sorry, it seems like we are talking
past each other…
For example you can't hoist a memory operation before a shared load or
after a shared store.
Well, to be picky, that depends on what kind of memory operation you
mean – moving non-volatile loads/stores across volatile ones is
typically considered acceptable.
In D that's fine (as long as in-thread SC is respected) because
non-shared vars are guaranteed to be thread-local.
But still, you can't move memory operations across any other arbitrary
function call either (unless you can prove it is safe by inspecting the
callee's body, obviously), so I don't see where atomicLoad/atomicStore
would be special here.
It is special because e.g. on x86 the function is often a simple
unprotected load or store. So after the inliner has at it, there's
nothing to stay in the way of reordering. The point is the compiler must
understand the semantics of acquire and release.
Andrei
